Our main research subject is quantum materials driven far away from equilibrium by external fields such as laser light. The aim is to seek for new laws of physics that govern such exotic states and to find a way to control their collective dynamics. We employ new theoretical frameworks such as Floquet engineering which enables us to understand nonequilibrium physics with the depth comparable to equilibrium systems. We can also obtain important insights from other existing research fields such as turbulence, neural network, and non-linear semiconductor optics, and apply them to new exotic materials. The target materials range from topological systems to strongly correlated systems (Fig. 1). New non-linear response phenomena such as the heterodyne Hall effect (Fig. 2), i.e. quantum Hall effect induced by oscillating magnetic fields, will be studied as well.

Fig. 1. Floquet engineering in quantum materials. T. Oka, S. Kitamura, Annu. Rev. Condens. Matter Phys. 10, 387-408 (2019).

Fig. 2. Heterodyne device utilizing Floquet states. (a) Frequency mixed output is realized. (b) A realization of the heterodyne Hall effect using 2D Dirac semimetals.

Research Subjects

Floquet engineering of quantum materials

Discovery of novel phenomena and law of physics in nonequilibrium systems

Scanning Tunneling Microscopy as a Single Majorana Detector of Kitaev’s Chiral Spin Liquid: M. Udagawa, S. Takayoshi and T. Oka, Phys. Rev. Lett.126, 127201 (2021).

h/e oscillations in interlayer transport of delafossites: C. Putzke, M. D. Bachmann, P. McGuinness, E. Zhakina, V. Sunko, M. Konczykowski, T. Oka, R. Moessner, A. Stern, M. König, S. Khim, A. P. Mackenzie and P. J. W. Moll, Science368, 1234 (2020).

3.

Non-perturbative terahertz high-harmonic generation in the three-dimensional Dirac semimetal Cd 3 As 2: S. Kovalev, R. M. Dantas, S. Germanskiy, J.-C. Deinert, B. Green, I. Ilyakov, N. Awari, M. Chen, M. Bawatna, J. Ling, F. Xiu, P. H. van Loosdrecht, P. Surówka, T. Oka and Z. Wang, Nature communications11, 1-6 (2020).